1. Field of the Invention
This invention is concerned with the protection of materials against the degradative effects of ultraviolet light.
2. The Prior Art
Certain organic materials which possess ultraviolet light absorbing properties can be added to many other organic materials to protect such substances from being degraded or damaged by ultraviolet light. For example, various polymers, plastics, resins, cosmetics, dyes, pigments, lacquers, varnishes, textiles, etc. are subject to photodegradation by sunlight or ultraviolet radiation and such materials are often protected by treatment with chemicals which will absorb the harmful rays and convert them to relatively harmless forms of energy.
An effective sunscreening agent must absorb large quantities of light in the ultraviolet portion of the suns rays which reach the earth, i.e. in the range of 290 to 400 nanometers. It should also, in addition to absorbing large quantities of ultraviolet light, be stable to U.V. radiation, be compatible with the medium into which it is incorporated, possess little or no color, be nontoxic, be thermally stable and have low volatility.
The prior art does not teach that substituted N,N'-bis-aromaticformamidines possess the outstanding light absorbing properties combined with high photo and thermal stability as disclosed in this invention.